Sir Alex Ferguson announced today that he is to retire as Manchester United manager at the end of the season, describing his 27 years in charge of the club as having been an 'honour and a privilege.'

The 71-year-old, who clinched his 13th Premier League title with the club last month paid tribute to his wife and colleagues for their support during his long tenure at Old Trafford.

But the announcement appeared to damage the club's value on the stock market with shares falling by 4.5 per cent in the hours that followed before rallying to -1.28 per cent.

Sir Alex said in a statement that it was important to him to leave the club in the 'strongest possible shape.'

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Retiring: Manchester United manager Sir Alex Ferguson has announced that he will step down after 27 years in charge of the club and 13 Premier League title wins

Cheerful: Ferguson in the Ibrox directors' box at the Rangers v Man United legends match this week

Success: Sir Alex pops a cork after winning the Premier League title last month, left, and is seen decked out in United colours after he was unveiled as their new manager in 1986

CLUB'S SHARE PRICES TUMBLE

Shares in Manchester United today fell in New York amid fears over the impact that Sir Alex Ferguson's departure will have on the club.

The opening bell on Wall Street saw shares down by 3 per cent, driven lower by worries over whether the club can appoint the right replacement for the most successful manager in English football history.

His successor will be the key figure at a business laden with almost £370 million of debt and tightly controlled by its US majority owners, the Glazer family.

The club, which trades under the MANU ticker on Wall Street, announced his departure while US markets were closed, but shares slipped on opening as investors digested the impact of the 71-year-old's departure on one of sport's most successful franchises.

In the prospectus to its 2012 stock market flotation, Manchester United warned: 'We are highly dependent on members of our management, coaching staff and our players.

'Any successor to our current manager may not be as successful as our current manager.'

Shares in the club have surged 34 per cent since floating in August at 14 US dollars (£9) per share, closing on Tuesday evening at 18.77 US dollars (£12.11).

The flotation allowed the Glazer family to sell 16.7m shares - equal to a 10 per cent stake.

The Glazers bought the Premier League football club for £790 million in 2005 in a controversial deal that enraged fans because they put in just £300 million of their own money and loaded the club with debt.

The club's most recent annual results showed total revenues of £320.3 million for the year to the end of June 2012, down 3.3 per cent on a year earlier.

Hargreaves Lansdown head of equities Richard Hunter said: 'The Manchester United merchandising machine will not grind to a halt overnight.

'The company is thinly traded and researched on Wall Street, but of the handful of analysts which cover the stock, the consensus of the shares as a buy is likely to remain intact, despite the inevitably difficult transition phase to a new chapter in the club's history.'

He said: 'The decision to retire is
one that I have thought a great deal about and one that I have not taken
lightly. It is the right time.

'It was important to me to leave an organisation in the strongest
possible shape and I believe I have done so.

'The quality of this league winning squad, and the balance
of ages within it, bodes well for continued success at the highest level whilst
the structure of the youth set-up will ensure that the long-term future of the
club remains a bright one.'

Sir Alex will remain part of the set up at Old Trafford despite stepping back from on the field matters.

He will take up a role as director and ambassador for the club when he retires after Manchester United's game with West Brom on May 18 - his 1,500th game in charge.

He said: 'Going forward, I am delighted to take on the roles of both Director and Ambassador for the club. With these activities, along with my many other interests, I am looking forward to the future.'

He paid tribute to the support of his friends, colleagues and family throughout his career, in particular his wife Cathy.

He said: 'I must pay tribute to my family, their love and support has been essential.

'My wife Cathy has been the key figure
throughout my career, providing a bedrock of both stability and
encouragement. Words are not enough to express what this has meant to
me.

'As for my players and staff, past
and present, I would like to thank them all for a staggering level of
professional conduct and dedication that has helped to deliver so many
memorable triumphs.'

Ferguson has had a career the like of which will never be seen again.

He won his 49th trophy by winning United's 20th league championship and seemed set to extend his career into next season, confirming as much in his programme notes ahead of Sunday's encounter with Chelsea.

Instead, with a hip operation booked in for August, this weekend's Old Trafford encounter with Swansea, followed by a trophy presentation, will be his last home game in charge.

Manchester united Chief Executive David Gill described his time working with the manager as the 'greatest experience' of his working life.

He said that the club have been planning for Sir Alex's retirement on and off the pitch.

He said: 'I've had the tremendous pleasure of working very closely with Alex for 16 unforgettable years - through the treble, the double, countless trophy wins and numerous signings.

Mr Cameron said on Twitter: 'Sir Alex Ferguson's
achievement at #MUFC has been exceptional. Hopefully his retirement will
make life a little easier for my team #AVFC.'

This afternoon he joked that Sir Alex will have to provide a consultancy service to Aston Villa, the side Cameron supports, as the midlands club have battled relegation this season.

In a speech opening debate in the Commons following the Queen's address today, Mr Cameron joked that even Conservative MPs would be recognising the achievements of Sir Alex - a staunch Labour supporter.

He said: 'It is the day to perhaps sing the praises of Sir Alex Ferguson, a remarkable man in British football who has had an extraordinary, successful career.

'I am sure that all members, even on the blue team, will want to pay tribute to this member of the red team. Perhaps he could now provide some consultancy services for Aston Villa.'

He said: 'I won't let this day pass without paying tribute to the most successful football manager this world has ever seen - a great supporter of the reds, you might call him.

'Sir Alex Ferguson, phenomenally talented at his job, winner of 13 championships - (he) can teach us all about hard work and dedication.'

Sir Alex had vowed to carry on 'indefinitely' in programme notes written before Sunday's defeat against Chelsea.

Devoted: Sir Alex and Cathy pictured with new born son Mark, left, and in the kitchen of their Glasgow home when he played for Rangers in 1968. Sir Alex thanked her for her support throughout his career

He arrived at the club's Carrington training ground to take training as normal this morning.

But already speculation is mounting as to who could replace the most successful manager in British football history.

Talks are underway to find a replacement and Everton manager David Moyes is among the frontrunners.

It
had been rumoured that Moyes would initially join the club as
understudy to Ferguson for a season before taking over the reigns full
time.

Moyes remains the favourite to take over with bookmakers offering odds of 4/6 this morning.

Other big names thought to be in the
running include Real Madrid manager and former Chelsea favourite Jose
Mourinho, who is tipped at 6/5 by bookmakers to get the job.

The self-proclaimed 'special one' has been widely tipped to join Chelsea, but could be set to rethink those plans.

Officials at
Old Trafford had put up a wall of silence before this morning's announcement, despite heavy speculation.

The club were not even taking calls from journalists last night amid a frenzy
of speculation over their manager’s future.

Similarly the club will have to announce Sir Alex's successor to the market as soon as he is appointed.

Sources say that there is expected to be 'an announcement within days.'

Ferguson was expected at Chester Races today for a planned day out with some of United’s players.

But while some of the side's stars, including Wayne Rooney and Danny Wellbeck were spotted, their manager was nowhere to be seen.

Rumours began to circulate on Tuesday
among United’s players and coaching staff, who were involved in a golf
match at Dunham Forest in Cheshire.

The Scotsman became famed throughout his career for his infamous 'hairdryer treatment' dished out to players and his fiery temperament.

One of the most infamous examples of star players feeling Ferguson's wrath came in February 2003 when the manager kick a boot in the changing room which hit David Beckham on the forehead.

Beckham wore the wounds from the incident in a very public fallout and left the club months later.

Things could have turned out very differently for Ferguson and Manchester United had the club not won the FA Cup in 1990.

Ferguson's side were struggling in the league and had a tough third round tie against Nottingham Forest.

If the tabloids were to be believed then Ferguson would have been sacked if the team finished trophyless.

But a goal by youth team product Mark Robins gave United a win and the rest is history.

Moyes was at Goodison Park on Tuesday night to watch Everton defeat Newcastle in the Under 21s Premier League.

The 50-year-old Scot is out of
contract this summer but has refused to discuss his future publicly,
insisting only that he would weigh up his options at the end of the
season.

United’s final match of the season, at West Bromwich Albion on May 19, will be the 1,500th of Ferguson’s tenure as manager.

'FOOTBALL...BLOODY HELL!' MEMORABLE SIR ALEX FERGUSON QUOTES

Sir Alex Ferguson has been involved in some of the most exciting moments in British football history and has provided the media with some of the most memorable quotes. Here are a selection of the very best.

'I can't believe it. I can't believe it. Football. Bloody hell.'After winning the Champions League final against Bayern Munich on May 26, 1999.

'It's getting tickly now - squeaky-bum time, I call it.'During the 2002/03 end-of-season title race between Arsenal and United.Sealed with a kiss: Sir Alex Ferguson toasts Manchester United's 1999 Champions League success

Outspoken: Sir Alex has offered the press a number of memorable quotes over the years

'He was certainly full of it, calling me "Boss" and "Big Man" when we had our post-match drink after the first leg. But it would help if his greetings were accompanied by a decent glass of wine. What he gave me was paint-stripper.' - On Jose Mourinho.

'It was a freakish incident. If I tried it 100 or a million times it couldn't happen again. If I could I would have carried on playing!'Explaining how he kicked a boot in the United dressing room that hit David Beckham in the face.

'When an Italian tells me it's pasta on the plate, I check under the sauce to make sure. They are the inventors of the smokescreen.'Before playing Inter Milan in the Champions League quarter-final, 1999.

'My greatest challenge is not what's happening at the moment, my greatest challenge was knocking Liverpool right off their ******* perch. And you can print that.'On Alan Hansen questioning his future in 2002.

That's handy: Everton boss Moyes is leading the betting to replace Ferguson at Old Trafford

'THANKS BOSS': DAVID BECKHAM'S MESSAGE TO HIS BEST MANAGER

'I've just seen the news on Sir Alex. As I have said many times before the boss wasn't just the greatest and best manager I ever played under he was also a father figure to me from the moment I arrived at the club at the age of 11 until the day I left.

'Without him I would never have achieved what I have done in my career. He understood how important it was to play for your country and he knew how much it meant to me.

'After '98 without the manager I would have found it virtually impossible to cope with the attention I was getting on and off the field and for this I will always be grateful to him for his support and protection.

'I am truly honoured to have been guided by the greatest manager in football and to have had the career that I had under him.Thank you boss and enjoy the rest!'

On Twitter, Rio Ferdinand echoed his former teammate's sentiment, saying: 'The bosses work ethic, his desire to win + to make us better players were unrivalled. Thanks boss.'

Many people inside football —
including two Premier League managers — have suggested privately this
season that Ferguson would have stepped aside had United not lost last
season’s Premier League title race to Manchester City on the last kick
of the campaign.

That has never been confirmed by United but it is
thought Ferguson broke the news to his wife, Cath, that he had to shelve
plans to retire within hours of City snatching the title.

There were also suggestions that
Ferguson’s brother Martin may be standing aside from his scouting
duties.

Of similar significance was the decision by David Gill —
Ferguson’s closest ally — to step down as chief executive at the end of
this season. But it had emerged United were preparing to make a more
seismic announcement.

At the weekend, Ferguson suggested in his programme notes he would be around at Old Trafford next season.

Having always cited his health as the
primary factor in any decision to retire, the club’s confirmation last
Friday evening that Ferguson, who had a heart pacemaker fitted in 2004,
would undergo hip surgery in August raised fresh doubt over his
determination to continue in the post.

The developments came on the back of
fevered and persistent betting this week that British football’s most
successful manager may be ready to step aside.

Conquering Europe: Fergie lifts the Champions League trophy in Moscow in 2008

Double top: Fergie, holding a BBC Lifetime Achievement Award, with David
Beckham at SPOTY in 2001

Unlucky for some: Ferguson has got his hands on a the Premier League trophy a remarkable 13 times in all

‘I don’t have any plans at the moment
to walk away from what I believe will be something special and worth
being around to see,’ he said.

‘It’s always difficult in football to
be absolutely sure of the future because the game has a habit of
tripping you up, but I don’t live in a fantasy world and believe we have
every reason to feel confident about the future of Manchester United.

'My view stems not from the euphoria of winning back the title we lost
last season, but on the way we did it and the make-up of our playing
personnel.’

Glory days: Sir Alex pictured with the Champions League and Premier League trophies

Finest hour: Manchester United secured a treble of Champions League, Premier League and FA Cup in 1999

Already bookmakers seem to be predicting a slight decline in the fortunes of the club on the pitch after Sir Alex retires.

Bookmakers
have already lengthened odds of the club retaining its Premier League
crown next season, with Manchester City now installed as firm
favourites.

William Hill spokesman Joe Crilly said: 'Sir Alex has been the bane of bookmakers for 27 years but his leagcy is such that whether Mourinho or Moyes, or anyone else for that matter, takes the job, they

will still be considered very realistic Premier League challengers.

'Having said that, no one knows how to build a title winning side like Sir Alex and for that reason we have had no option but to ease the price of the Reds winning the League next season.'

The odds on Sir Alex claiming the BBC Sports Personality of the Year Award in December have been dramatically slashed following this morning's news.

He was considered an outsider at 33/1 yesterday, but is now second favourite behind fellow Scot Andy Murray at 6/1.

Betting punters have clearly been swept up in the speculation as to who should take over at Old Trafford with £50,000 staked at Ladbrokes this morning alone.

One gambler laid out £1,000 that Mourinho will succeed Sir Alex as manager.

A spokesman for Ladbrokes said today: We've had a bet every second and there's no sign of it slowing down any time soon.'

JOSE MOURINHO (ODDS: 4/1): Many had believed it was all but a done deal that the
Real Madrid boss would return to Chelsea at the end of the season.

But
the Portuguese, while clearly hinting he is keen to manage in England
once again, has never explicitly mentioned his old club.

Despite a
lukewarm endorsement from United legend Sir Bobby Charlton, Mourinho is
the one man guaranteed not to be overwhelmed by taking on the challenge
of following Ferguson.

OLE GUNNAR SOLSKJAER (ODDS: 25/1): A host of former United players have been linked with the job in the past yet all have fallen by the wayside.

Legend: Ole Gunnar Solskjaer celebrating scoring the winning goal for Manchester United during the European Champions League Final against Bayern Munich in 1999 could replace Sir Alex

The latest is Solskjaer, who has made a successful start to his managerial career at Molde. He lacks experience, though, and will benefit from Ferguson remaining at the club as a director.

JURGEN KLOPP (ODDS: 20/1): The Borussia Dortmund boss has made a big impression during his club's impressive run to the Champions League final.

With a style of football that seems tailor-made for the English football and an at-times eccentric manner in his post-match interviews, he would be an intriguing addition to the Premier League.

LAURENT BLANC (ODDS: 50/1): Blanc had a brief stint with the Red Devils at the end of his career, so knows the club well.

Caught the eye as manager of Bordeaux, where he won the French league title, then stabilised a France team that collapsed into chaos at the last World Cup before stepping down following their quarter-final loss to Spain at Euro 2012.

FERGIE'S FIVE FINEST SIGNINGSWHO TOOK UNITED TO THE TOP OF EUROPE

Top of the stoppers: Peter Schmeichel

Peter Schmeichel (signed from Brondby, 1991)

Widely regarded as the greatest goalkeeper in Premier League history,
the Dane's heroic efforts provided clean sheets aplenty and the security
at the back which was so key to United's success throughout the 1990s.
Schmeichel, recruited for around £500,000, knew how to intimidate
opposition strikers by making optimum use of his frame and at times
appeared just as fearful for his defenders, who would frequently receive
a rollicking from him. Capped eight glorious years with the club by
skippering United - in the absence of the suspended Roy Keane - in the
1999 Champions League final as Ferguson's men secured the treble.

Eric Cantona (signed from Leeds, 1992)

Cantona's
five-year spell at United will never be forgotten. The Frenchman, who
cost Ferguson just over £1million, gave the club's fans many a moment to
savour on the pitch with his dazzling skills, which helped the Red
Devils to a haul of four Premier League titles and two FA Cups. But what
perhaps cemented his iconic status was the way he played the part of
the tortured genius. The most infamous instance of his short temper was
the kung-fu kick he aimed at a Crystal Palace supporter and he made
philosophical comments afterwards about seagulls following a trawler. It
was somewhat appropriate that he exited early leaving the crowd wanting
more, retiring aged 30 in 1997.

Driving force: Roy Keane

Roy Keane (signed from Nottingham Forest, 1993)

The
£3.75million Ferguson paid Forest for Keane was a British transfer
record at the time, but there is little question that he got value for
money. In 12 years of service, the Irish midfielder was United's engine
room and driving force as they dominated English football through the
1990s and into the next decade. He also led them to the 1999 Champions
League final, only to miss the game through suspension. Keane succeeded
Cantona as captain and was just as combustible a character, if not more
so. But it was that edge on the field that so endeared him to United
fans and made him the player everyone else wanted in their team.

Cristiano Ronaldo (signed from Sporting Lisbon, 2003)

Megastar: Cristiano Ronaldo

Ferguson signed a teenage Ronaldo for
£12.24million and it looked as if he may have paid over the odds for
little more than a showboater in the early days of the Portuguese
forward's United career. He soon showed his game was not just about
stepovers, though, developing into one of the world's most potent
players. Ronaldo scored an incredible total of 42 goals for the club in
the 2007-08 season as the Red Devils won the Champions League. Although
his exit to Real Madrid a year later was a blow, the world record
£80million fee he commanded softened it considerably.

Edwin van der Sar (signed from Fulham, 2005)

Van
der Sar was 34 when he arrived at Old Trafford for an undisclosed fee,
but the Dutch goalkeeper was in no way a fading force. It soon became
apparent that Ferguson had finally found the solution in a position
which had been a problem for United since Schmeichel's departure, as Van
der Sar's reliable hands helped the team achieve a new period of
success. He broke a multitude of records with his clean sheets in the
2008-09 season and finally retired from football in 2011, having won
four Premier League titles and the Champions League with the Red Devils.